This invention relates to cartridges having a supply reel and a take-up reel for carrying an inked ribbon which is translated from reel to reel. More particularly, this invention relates to inked ribbon cartridges having a ribbon tension control device included therewithin.
Inked ribbon cartridges are known which supply an inked ribbon to a printing station of an associated printing device, e.g., a rotary printer or a typewriter. In typical devices of this type, the cartridge is provided with a supply reel about which the ribbon is wound, a take-up reel for storing used portions of the ribbon, and a drive mechanism for advancing the inked ribbon from the supply reel past the printing station and onto the take-up reel.
In order to maintain the print quality of the characters printed at the station substantially uniform, the tension of that portion of the inked ribbon located in the printing station must be maintained substantially constant in order to preclude stretching or contracting of this portion of the ribbon. Among other factors, the extent to which the ribbon is stretched or contracted is dependent upon the pulling force required to withdraw fresh ribbon from the supply reel. In typical cartridges, this pulling force is not constant, but varies with the quantity of ribbon remaining on the supply reel.
Since an inked ribbon cartridge is normally designed as a disposable item, any ribbon tensioning mechanism should preferably embody a minimum number of working elements in order to maintain the manufacturing cost at a minimum, while at the same time must provide substantially uniform tension at the printing station, regardless of the amount of the inked ribbon which has been removed from the supply reel. In addition, the ribbon tensioning mechanism must not alter the ink density of the ribbon as it is payed out from the supply reel, since such alteration can readily result in printed characters of varying density. To date, efforts to design a low cost inked ribbon cartridge meeting the above criteria have not met with wide success.